AbstractMicroglia have classically been viewed as the endogenous phagocytes of the brain, however, emerging evidence suggests roles for microglia in the healthy, mature nervous system. We know little of the contribution microglia make to ongoing processing in sensory systems. To exploreIba1+microglial diversity, we employed the inferior colliculi (IC) as model nuclei, as they are characterized by sub-regions specialized for differing aspects of auditory processing. We conducted fluorescent multi-channel immunohistochemistry and confocal microscopy in guinea pigs of both sexes and discovered that the density and morphology ofIba1+labelling varied between parenchymal sub-regions of IC, whileGFAP+labelling of astrocytes was confined to theglia limitans externaandperi-vascular regions. The density ofIba1+microglia somata was similar across sub-regions, however a greater amount of labelling was found in dorsal cortex than ventral central nucleus or lateral cortex. To further understand these differences between sub-regions in IC, Sholl and skeleton analyses of individual microglia revealed a greater number of branching ramifications in dorsal cortex. We also quantified abutments ofIba1+microglial processes ontoGAD67+(putative GABAergic) somata. Cluster analyses revealed two novel sub-types ofGAD67+neuron, which can be distinguished solely based on the quantity of axo-somaticIba1+abutments they receive. These data demonstrateIba1+microglia exhibit different morphologies and interactions withGAD67+neurons in distinct sub-regions of the mature, healthy IC. Taken together, these findings suggest significant heterogeneity amongst microglia in the auditory system, possibly related to the ongoing functional demands of their niche.